One conventional method of providing an interior trim component of a motor vehicle involves heating a planar plastic sheet of cover material (also known as sheet-stock or roll-stock) that is pre-textured with the desired surface texture, which may particularly be a simulated leather grain. This pre-textured cover material is then drawn over a pre-shaped substrate coated with a pressure-sensitive adhesive during a male vacuum forming process, and bonded thereto by the adhesive to provide the interior trim component.
During the foregoing molding process, as the plastic sheet is stretched and drawn over the pre-shaped (three-dimensional) contour of the substrate, the pre-textured cover sheet is distorted differently at different areas, depending on the degree of stretching and molding that has taken place at the respective areas. More particularly, an area that is more deeply or extensively drawn and stretched will suffer from greater distortion and texture (grain) loss. Another problem with the foregoing process is the use of pressure sensitive adhesives, which may contain volatile organic compounds (VOCs) or reactive chemistries which are environmentally unfriendly.
In order to potentially reduce the foregoing difficulties of grain loss, U.S. Pat. No. 6,749,794 to Spengler sets forth an automobile interior trim component which includes a substrate formed or laminated onto a pre-molded cover sheet including a foam backing and a skin film having a surface texture. To start the process, the cover sheet is preheated as a planar sheet so the skin film is in a melted viscous liquid state above its melting temperature, and the foam backing remains in a solid elastic foam state below its melting temperature. The preheated cover sheet is then mechanically pre-molded by a back mold into a front mold. Pressurized air is applied through the back mold, to blow-mold the cover sheet against the front mold, so the melted skin film reproduces a surface texture of the front mold surface while the solid foam backing acts as a buffer and air barrier layer. Vacuum is also applied through the front mold surface.
In a subsequent step, the mold is opened, and the pre-molded cover sheet with a finished textured skin may be removed for further separate use, or a substrate may be molded and laminated onto the back surface of the foam backing of the molded cover sheet directly in the same molding apparatus.
In forming a substrate onto the back surface of the foam backing of the cover sheet directly in the same molding apparatus, Spengler discloses that the substrate material may be a pre-heated sheet of a composite of polyolefin fibers, such as polypropylene fibers, and natural fibers or glass fibers or polyester fibers or the like, or may be a polyurethane foam, which has been preheated by any conventionally known means and which is carried or positioned in the molding apparatus by any conventionally known means.
In order to mold and laminate the substrate onto the back surface of the foam backing, the back mold is driven upward and/or the front mold is driven downward so that the back mold presses and molds the substrate against the back surface of the foam backing of the previously molded cover sheet. During forming of the substrate, the pre-heated and at least partly melted fibers of the substrate undergo melt bonding with the still-warm or still-hot foam backing of the cover sheet, so that the substrate is integrally bonded onto the cover sheet without requiring any additional adhesive or the like therebetween.
Unfortunately, while bonding of the substrate to the cover sheet may be performed without requiring use of an adhesive, bonding of the substrate to the cover sheet necessarily requires opening and closing the mold for a second time after forming the pre-molded cover sheet, which delays the manufacturing process and increases cost. Furthermore, pressing and molding the substrate against the back surface of the foam backing of the previously molded cover sheet while the molded cover sheet is still hot may cause further reproduction of the surface texture of the front mold surface into the skin film, which may result in defects if the additional surface texture reproduction does not perfectly coincide with the first surface texture reproduction (e.g. ghost marks).
In order to avoid the sequential molding operation of Spengler, it may be possible to mold a substrate directly against the back surface of the foam without reopening and reclosing the mold, such as by forming the substrate by thermoplastic injection molding directly to the decorative cover sheet. However, to accommodate such thermoplastic injection molding, the foam backing must be made of a material which may withstand the heat and pressure of the injected polymer melt without melting or distorting.
What is needed is a manufacturing process for a decorative article which aims to overcome the aforementioned difficulties and drawbacks of the art.